This invention relates to electrical power supplies and more particularly to laminar cells and batteries.
U.S. Pat. Nos. 3,705,543; 3,543,662; 3,543,663 and 3,595,661 relate to photographic film packs comprising an enclosure containing self-developing film units integrated with a battery comprising the power supply for a camera adapted to expose and process the film units. Such film packs are presently employed in automatic cameras such as that sold by Polaroid Corporation of Cambridge, Mass., U.S.A. under the trademark SX-70.
Batteries suited for use in systems such as that just described are required to supply high current drains with low internal impedance. These requirements have led to the use of thin, flat laminar batteries. A particular battery long used for this purpose uses zinc anodes, cathodes of manganese dioxide and carbon, and an aqueous zinc chloride-ammonium chloride electrolyte.
In an effort to provide improved batteries, investigations have been made into electrochemical cells other than the zinc anode/manganese dioxide cathode system referred to above. One such system involves a cadmium anode with a suitable cathode such as manganese dioxide. See, e.g., U.S. Pat. Nos. 3,494,796 and 3,775,273. These systems are reputed to have a satisfactory storage stability. However, attempts to fabricate the cadmium anode in a suitably thin form generated problems.
The prior art has heretofore formulated electrodes by electroplating cadmium onto various metal foils. See, e.g., U.S. Pat. Nos. 3,326,721, 3,783,025 and 3,837,919. The dimension requirements of the present batteries, however, are such that the cadmium cannot be plated on an iron or zinc foil without the formation of a substantial number of pinholes. Minor leaks of electrolyte through the cadmium plate and into contact with the iron or zinc foil result, and since the iron or zinc is electrochemically active in the cell environment, corrosion problems arise and the requisite storage stability cannot be achieved.
It has now been found that if the foil is a lead foil, a very thin cadmium plate can be deposited without any substantial number of pinholes and, further, since the lead is electrochemically inactive in the cell environment, minor leakage of the electrolyte through the cadmium plate can be tolerated. As a result, battery cells and batteries can be fabricated having excellent storage stability.
Accordingly, it is the object of this invention to provide a new anode construction which can be used in battery cells and batteries meeting all of the foregoing electrical requirements and having a long storage stability period. This and other objects of the invention will become apparent to those skilled in the art from the following detailed disclosure.